I know this is subjective, but the principle "should be of interest to mathematicians" trumps. (I hope.)

Perhaps this should be a community wiki question. - GMRA

(3)
A useful feature of Math Overflow on a post like this one is the ability to sort answers chronologically as well as by number of votes. Just click the "newest" tab above the answers to see the most recent additions. - Anton Geraschenko

(10)
Since this thread continues to interest people, a request: Do people know more jokes that are erudite? That is, jokes that are related to interesting mathematics in some way. (Not necessarily very abstract mathematics.) The Banach-Tarski joke below is a good example, in my opinion. - Greg Kuperberg

(19)
I just voted this -1, and I'd like to see the question closed. People have had over a month to enjoy it, and its continued presence on the front page seems to encourage people to post very soft questions. This takes Math Overflow in what I think is a bad direction. - Tom Leinster

(64)
I disagree with Tom. I think some levity is desirable, and MO shouldn't all be serious business. - Richard Dore

(13)
With respect to the title, "No." - Harry Gindi

(1)
I agree with Tom, and I'm voting to close. - S. Carnahan

(19)
I've decided to finally put this one out of its misery. All that's happening now is people add new, mostly lame, jokes at the the end, which no one ever reads, and as a result the question keeps bouncing back to the front page. It's time to die. Closed. - Scott Morrison

(6)
I'd like to note my dissent with Tom and Scott on this. - Kevin McGerty

(7)
Why close a question with 35 upvotes and 49 stars? If those don't count, what the heck are they for? - Dr Shello

(5)
I've voted to reopen. I've taken a look at the last few posts. True, some of them are lame (to my taste), but some are good (again, to my taste; I quite liked the one about the exponential). - algori

Jokes are cutting-edge mathematics?. This may be more on-toppic at Mathemtics.SE. - Abhimanyu Pallavi Sudhir

(12)
The Pigeonhole Principle: If there are n pigeons and n+1 holes, then at least one pigeon must have at least two holes in it. - Bhaskar Vashishth

Q: How do you fit 32 people into a car with 5 empty seats? A: Put a log in front of it. (Joke credit: M. Gopalkrishnan) - Daniel Moskovich

(4)
I lolled so hard at the pigeonhole principle joke. Can't add an answer so I'll just add it here. This is more of a pick-up line than a joke. Proud(?) to say I came up with this one. Anyway: "Hey baby, are you the discrete topology? 'Cause you are strictly finer than all others." - tilper

Here's one from a former prof. A farmer sees his cows' milk production begin to decline. A team consisting of an engineer, a chemist, and a mathematician is assembled to optimize production. After months of working they present their results. The engineer says, "I've created this device which will maximize milk production from each cow." After the engineer's presentation, the chemist says, "I've created this special drink which, when consumed by the cow, will maximize her milk production." After the chemist's presentation, the mathematician begins, "First, assume we have a spherical cow..." - tilper

Mike's last joke reminded me of this one: a comathematician is a device for turning cotheorems into ffee.

(54)
For a while I've been wondering what mbinatorics would be, if it existed. Presumably it would be useful for mputer science. - Michael Lugo

(28)
One of these days I'm going to write a paper on "efficient corings". - Loop Space

(91)
AJ Tolland is fond of saying that what we really need is a machine for turning some of those theorems back into coffee. - Noah Snyder

(98)
I disagree. Mputer science would be useful for mbinatorics, not the other way around. - Boris Bukh

(110)
Ribet once told me that he was sent a generic UG textbook by a publisher for free, with the suggestion that he use it in his UG course. He decided not to, and took the book to Black Oak Books (2nd hand book store in Berkeley) and sold it for a few $$. On the walk back to the department he bought some coffee with the money, and then realised to his amusement that he'd done precisely what Noah mentioned above. - Kevin Buzzard

(6)
Sadly, Black Oak Books is no more :-( - Dan Piponi

(92)
I think I'm going to have to start referring to "cocoa" as "a". - Ian Morris

(11)
I have been told that in a lecture to physicists someone asked what was the name of object to which a Coxeter group is dual... - Mariano Suárez-Álvarez

(7)
In Chinese, the dualization of an object should be called 西东。 Right? (An explanation for non-speakers will not make it funny, sorry.) - Elizabeth S. Q. Goodman

(5)
Long years ago I've introduced and published notion "ver" (in a paper on topological dimension in a somewhat abstract Birkhoff lattice setting; then at least one more author used my "ver" too). The dual to "ver" is "cover". - Włodzimierz Holsztyński

(22)
I have no doubt now that coconuts are nuts. - Michael

Oh, what the hell, have another gold badge! :) - Asaf Karagila

(1)
I'd like to add here that a 2-mathematician is a mapping between two ways of turning coffee into theorems. - Fosco

(2)
I have a cat named Coco. Is her name properly just an empty string? - Michael Lugo

A topologist is someone who doesn't know the difference between his ass and a hole in the ground but does know the difference between his ass and two holes in the ground.

I went to visit him while he was lying ill at the hospital. I had come in taxi cab number 14 and remarked that it was a rather dull number. "No" he replied, "it is a very interesting number. It's the smallest number expressible as the product of 7 and 2 in two different ways."

(64)
I could not stop laughing after reading the Ramanujan joke. - Steven Gubkin

(66)
As for topology, I prefer the one about a topologist drinking tea. It goes like that. A topologist is drinking tea from a cup when suddenly the handle drops off. The topologist is amazed: the new shape is different but he can still drink tea from it. And so he does until the bottom of the cup drops off. Now he is totally befuddled: the shape is equivalent to the original one but how can he drink his tea now? - fedja

(13)
There's a (true) legend about an exam of linear algebra for engeneering students, in which the professor asked: "How many eigenvalues does an $n\times n$ matrix have?" and the student answered "Well... $n\cdot\sqrt{2}$". - Qfwfq

(41)
I've heard it as "how many elements are there on the diagonal of a $n\times n$ matrix?" "Uhm... $n\sqrt{2}$. - Federico Poloni

(12)
We had (almost) the same example: What examples of vector space did the teacher show you? $\mathbf R^3$? -- No -- Then $\mathbf R^2$? -- Neither. --- So what? --- $K^n$. - ACL

It's not the student's fault. The lecturer should have mentioned the scope of the assignment! - RP_

@lhf It's still funny. - silvascientist

(1)
@FedericoPoloni : Assuming that the matrix is diagonalizable, the questions are equivalent. - Toby Bartels

3

[+138]
[2009-10-19 06:35:14]
Anton Geraschenko

Here's one I came up with a few years ago that I'm quite proud of.

Q: What do you get when you cross a chicken with an elephant?
A: The trivial elephant bundle on a chicken.

(2)
I heard this from Rob Easton (I think) several years ago, I also found it hilarious. Again, thank you. - Karl Schwede

(112)
What do you get when you cross a citrus fruit with a bull? The trivial lime bundle on a taurus. - Michael Albanese

This is so good it makes me envision a day when there is a prize at the ICM for best jokes, or maybe at least they let someone this clever come out and warm up the crowd before a talk! anyway thank you for this, the only math joke i can remember. I just wish I could figure out how to tell it to a non mathematician. - roy smith

4

[+128]
[2009-10-19 17:19:06]
Mike Stay

Here are a few of my own inventions:

Old Macdonald had a form; ei /\ ei = 0

Save the environment: use continuation passing style!

What shape of pasta takes the least time to eat? Brachistochroni!

You might be a mathematician if you think fog is a composition.

The Yoda embedding, contravariant it is.

How are Goethe's Faust novels like isomorphisms of sets? Dey're de monic epics.

I'm kind of in two minds about this whole Schroedinger's cat thing...

qwhine, n. self-recrimination

recursive: (λ damn. damn (damn)) (λ damn. damn (damn))

Coeschatology: the study of the beginning of times. The coend is ming!

(17)
The first one is just awesome! Please keep inventing! - Armin Straub

fog is a composition in AMS Symbols alright. The circle used for composition sign in LaTeX is a bit larger than what some of us would wish. - Jose Capco

(32)
the yoda joke is great!! - Martin Brandenburg

I love these jokes because they connect mathematics to culture. - Olga

@MartinBrandenburg I've seen the yoda one before. I think it was in Ravi Vakil's Algebraic Geometry notes - Praneet Srivastava

Yes, but he didn't write the first version of those notes until a year after this (widely read) post appeared. I know that some jokes are so obvious that they get reinvented multiple times, but this one is both so obscure and so stupid that I'm pretty sure he got it from here. - Mike Stay

5

[+128]
[2009-10-30 23:44:19]
Jason S

an anecdote about David Hilbert from the wonderful book (for us laymen ;-)
Prime Obsession
[1]:

Hilbert had a student who one day presented him with a paper purporting to prove the
Riemann Hypothesis. Hilbert studied the paper carefully and was really impressed by
depth of the argument; but unfortunately he found an error in it which even he could
not eliminate. The following year the student died. Hilbert asked the grieving
parents if he might be permitted to make a funeral oration. While the student's relatives
and friends were weeping beside the grave in the rain, Hilbert came forward.
He began by saying what a tragedy it was that such a gifted young man had died
before he had had an opportunity to show what he could accomplish. But, he continued, in
spite of the fact that this young man's proof of the Riemann Hypothesis contained
an error, it was still possible that some day a proof of the famous problem would
be obtained along the lines which the deceased had indicated. "In fact," he continued
with enthusiasm, standing there in the rain by the dead student's grave, "let us consider
a function of a complex variable...."

[1] http://books.google.com/books?id=qsoqLNQUIJMC&pg=PA186

(3)
I wonder what Hilbert's dying speech/will was. It probably went along those famous lines... "let us consider a function of a complex variable..." - Simply Beautiful Art

6

[+124]
[2009-12-04 18:48:00]
Felipe Voloch

A British mathematician was giving a talk in Grothendieck's seminar in Paris. He started "Let X be a variety...". This caused some talking among the students sitting in the back, who were asking each other "What's a variety?". J.-P. Serre, sitting in the front row, turns around a bit annoyed and says "Integral scheme of finite type over a field".

(13)
I don't get it... - Kevin H. Lin

(17)
It's a dig at an attitude of dealing with abstract concepts without looking at concrete examples first, obviously exaggerated for effect. You need to know some algebraic geometry to understand the punch line. - Felipe Voloch

(3)
That's pretty funny. - Keenan Kidwell

(30)
It is a well-established tradition in France to keep the (scheme-theoretic, what else ?) definition of "algebraic variety" in limbo, just to keep the students from getting bogged down into concreteness :-) - Simon Pepin Lehalleur

(7)
The joke seems to presuppose the distinction between scheme and prescheme. - Lennart Meier

(6)
No, no, Illusie told me once that nobody knows what a variety is. And he is right! Some require them to be separated, other want them to be connected, or integral, or even geometrically integral. - ACL

(1)
Further to ACL's point, before scheme theory a variety had to be over an algebraically closed field. Serre's answer shows how that changed. - Colin McLarty

(1)
Is this a real story? - Henry

(7)
@SunghyukPark Yes. Confirmed by Serre. - Felipe Voloch

7

[+122]
[2009-10-19 05:18:50]
Sam Derbyshire

I like this one:

A mathematican walks into a bar accompanied by a dog and a cow.
The bartender says, “Hey, no animals are allowed in here!”
The mathematician replies, “These are very special animals.”
“How so?”
“They’re knot theorists.”
The bartender raises his eyebrows and says, “I’ve met a number of knot theorists who I thought were animals, but never an animal that was a knot theorist.”
“Well, I’ll prove it to you. Ask them them anything you like.”
So the bartender asks the dog, “Name a knot invariant.”
“Arf! Arf!” barks the dog.
The bartender scowls and turns to the cow asking, “Name a topological invariant.”
“Mu! Mu!” says the cow.
At this point the bartender turns to the mathematican and says, “Very funny.” With that, he throws the three out of the bar.
Outside, sitting on the curb, the dog turns to the mathematican and asks, “Do you think I should have said the Jones polynomial instead?”

(17)
which is the variant of the encient: "Who was the greatest baseball player that ever lived?" "Ruth!" barked the dog. "Okay, that's it!" says the bartender, and physically throws both man and dog out the door and onto the street. Turning to the man, the dogs shrugs and says, "Dimaggio?" - David Lehavi

(3)
You joke is due to Joel Hass, I believe. - Ryan Budney

8

[+116]
[2009-12-23 06:35:07]
Darsh Ranjan

jose's post reminds me of one I heard Michael Hutchings tell during an undergraduate calculus lecture:

$e^x$ was walking down the street one day and met a polynomial running in the opposite direction.

"Wait, why are you running?" asked $e^x$. The polynomial said:

"There's a differential operator over there! It could differentiate me and turn me into zero!" And the polynomial continued running in fright.

"Ha ha," $e^x$ said to himself. "I'm $e^x$! Let them differentiate me as many times as they want, it makes no difference to me!" So $e^x$ walked on and reached the differential operator. He confidently introduced himself: "Hi, I'm $e^x$!" The reply:

(20)
The first joke to me sounds like a debased version of the following joke, which was quite topical in about 2004: "Q: What's the value of the contour integral around the British Isles? A: Zero, because all the Poles are removable". This refers to the fact that at the time the joke was coined, Britain was host to a large number of Polish migrant workers who were in the unusual position of being intra-EU migrants not having indefinite leave to remain in Britain. - Ian Morris

(8)
I would imagine the variant given was around before 2004. - Sean Tilson

(1)
The Banach-Tarski paradox is all about the free grape. - Gene S. Kopp

Knuth appears to be unaware of a well-known $O(1)$ schema, which is unfortunately hard to date, but definitely predates the 1975 result he quotes. - Emilio Pisanty

(18)
Here is a joke in the same vein as the Banach-Tarksi one. What does the B stand for in Benoit B. Mandelbrot? Benoit B. Mandelbrot. - Michael Albanese

(1)
I know Harrison Brown's version of the contour integral, which is then followed by "What's the value of a contour integral around eastern Europe?" with the same answer as Ian Morris's version. This was in the 1990s, but presumably it goes back to the 1940s. - Toby Bartels

And now with Brexit, the contour integral around the UK has become 0 once more. - Toby Bartels

11

[+94]
[2009-11-06 19:28:29]
fedja

Here is the one I heard recently.

Professor: What is a root of $f(z)$ of multiplicity $k$?

Student: It is a number $a$ such that if you plug it into $f$, you get $0$; if you plug it in again, you again get $0$, and so $k$ times. But if you plug it into $f$ for the $k+1$-st time, you do not get $0$.

(9)
Actually, I kind of like this in a serious way :) - David Corwin

(14)
If you differentiate the function each time in between plugging it in, then this is correct! - Toby Bartels

(9)
...or divide by $(z-a)$ in between... - Jonas Meyer

(1)
@DavidCorwin Somehow I feel like this is the best way to sum this up. - Michał Masny

couldn't stop laughing.. - Arun

12

[+90]
[2009-10-19 00:36:41]
Richard Dore

Q: How do you tell an extroverted mathematican from an introverted one?

A: An extroverted mathematician stares at your shoes when talking to you.

Does anybody know the origin of this joke? I'm thinking of citing it in an essay. - Jamie Weigandt

(8)
This can be found in Steven Krantz's A Primer of Mathematical Writing, page 159 (footnote). The exact quote from there is: An introverted mathematician is one who looks at his shoes when he talks to you. An extroverted mathematician is one who looks at your shoes when he talks to you. - KConrad

The path of love is never smooth
But mine's continuous for you
You're the upper bound in the chains of my heart
You're my Axiom of Choice, you know it's true

But lately our relation's not so well-defined
And I just can't function without you
I'll prove my proposition and I'm sure you'll find
We're a finite simple group of order two

I'm losing my identity
I'm getting tensor every day
And without loss of generality
I will assume that you feel the same way

Since every time I see you, you just quotient out
The faithful image that I map into
But when we're one-to-one you'll see what I'm about
'Cause we're a finite simple group of order two

Our equivalence was stable,
A principal love bundle sitting deep inside
But then you drove a wedge between our two-forms
Now everything is so complexified

When we first met, we simply connected
My heart was open but too dense
Our system was already directed
To have a finite limit, in some sense

I'm living in the kernel of a rank-one map
From my domain, its image looks so blue,
'Cause all I see are zeroes, it's a cruel trap
But we're a finite simple group of order two

I'm not the smoothest operator in my class,
But we're a mirror pair, me and you,
So let's apply forgetful functors to the past
And be a finite simple group, a finite simple group,
Let's be a finite simple group of order two
(Oughter: "Why not three?")

I've proved my proposition now, as you can see,
So let's both be associative and free
And by corollary, this shows you and I to be
Purely inseparable. Q.E.D.

When someone once asked Professor Eilenberg if he could eat Chinese
food with three chopsticks, he answered, "Of course," according to
Professor Morgan. The questioner asked, "How are you going to do it?"
and Professor Eilenberg replied, "I'll take the three chopsticks, I'll
put one of them aside on the table, and I'll use the other two."

[1] http://www.lehigh.edu/~dmd1/eilobit

(2)
Isn't this just obvious? - Michał Masny

16

[+84]
[2009-10-24 06:04:13]
aorq

My favorite one-liner:

Why did the mathematician name her dog "Cauchy"? Because he left a residue at every pole.

My favorite anecdote:

An engineer, a physicist, and a mathematician find themselves in
an anecdote, indeed an anecdote quite similar to many that you
have no doubt already heard. After some observations and rough
calculations the engineer realizes the situation and starts
laughing. A few minutes later the physicist understands too and
chuckles to herself happily, as she now has enough experimental
evidence to publish a paper. This leaves the mathematician
somewhat perplexed, as she had observed right away that she was the
subject of an anecdote and deduced quite rapidly the presence of
humor from similar anecdotes, but considers this anecdote to be
too trivial a corollary to be significant, let alone funny.

(6)
+1 for the one-liner. - Włodzimierz Holsztyński

I heard the anecdote before too, but the participants weren't assumed to be male. - Greg Martin

I would recommend that you use a gender-neutral occupational term, like we now often do for police offer, firefighter, chairperson, etc. Whether that recommendation was received as obvious, reasonable, progressive, or ludicrous would depend a lot upon the culture surrounding this language. In English, in today's culture, I think it's important to consider this issue. - Greg Martin

(2)
I have no recommendation for you. Are you asking because this is a situation you find yourself in, or anticipate doing so? Or is it a way of derailing my point about English in today's world? Giving you the benefit of the doubt, I'll assume the former. Good luck! - Greg Martin

A biologist, a physicist and a
mathematician were all drinking coffee
and tea and observing a house across
the street from them. They notice that
two people walk into the house and
then an hour later, three people walk
out.

Physicist: An experimental error. Our
first measurement was incorrect.

Biologist: No, they've obviously
reproduced.

Mathematician: No, now when a one
person enters the house, it'll be
empty again.

(2)
Can't believe this hasn't received more upvotes, it is one of the funniest - Trevor J Richards

but also most widely know, so no one cracks up about it any more. - peter

18

[+82]
[2009-10-21 01:54:54]
Darsh Ranjan

There's a mathematician whose non-mathematician friends are constantly ribbing him because his field is just so abstract and seems to have no relevance to the real world. One day, it gets to him, and he resolves to arm himself with some practical applications of research mathematics for the next encounter. He realizes that his own specialty (mathematical logic) is probably too far beyond them to be of any use there, so he goes to the department bulletin board to find an upcoming talk about something practical. Luckily, a talk is scheduled that afternoon on "the theory of gears." "Perfect!" he says. Nothing could be more practical, more down-to-earth. Finally, he'll be able to prove to his friends that mathematics is relevant to the real world. That afternoon, he's so excited that he goes to the talk five minutes early and sits in the first row of seats. Then, at the scheduled time, the speaker stands up and begins: "While the theory of gears with real numbers of teeth is well understood...."

(38)
This is pretty awesome. The best (worst?) part is, I would actually like to hear that talk. - DoubleJay

(37)
I just told this joke at a conference, except I flubbed it and said it was about gears with uncountably many teeth. Five minutes later, I found two of the listeners arguing about slippage in an explicit construction they had come up with. - Neil Toronto

19

[+79]
[2009-12-06 06:19:06]
ambrosiac

(From the unpublished manuscript "Mathematics in a nutshell":)

A coconut is just a nut

(13)
On a related note, a comathematician is a device for turning cotheorems into ffee. - Michael Lugo

(3)
and cocoa is just 'a' (stolen from a comment on another thread) - David Corwin

20

[+76]
[2009-12-06 06:48:07]
Kevin O'Bryant

Theorem: There are infinitely many composite numbers.

Proof: Suppose there are only finitely many, and multiply them together.

(11)
What if you do this in the ring of integers mod 6? - Ilya Grigoriev

(28)
It's crucial in the proof that you multiply the numbers together and do not add one! :) - Somnath Basu

(122)
What if there is only one composite number? - Douglas S. Stones

(3)
If there is zero composite number , multiply them all and you get one. This joke works I believe in French , German , Italian probably Spanish and many others. Trick question for a linguist: Find some language n which it does not work? What about finish ? - Jérôme JEAN-CHARLES

(31)
@ Douglas: There is also a long tradition, beginning with Euclid, of giving Euclid's proof without checking the set of primes is non empty. - roy smith

(34)
Roy, it's no problem: in that case, per Jérôme's observation, the trick “multiply them all and add 1” gives 2. - LSpice

(8)
so euclid began the convention that an empty product is 1? - roy smith

21

[+66]
[2009-10-19 14:18:26]
Anna Varvak

"Why did the chicken cross the Mobius band?"

The question isn't whether good math jokes exist, but whether they can be classified. The example above works because it plays on ones expectation of the "chicken crossing the road" jokes. Another one in the same vein, known as the shortest math joke:

"Let epsilon<0."

Another one, which I actually heard in class:

"Take a positive integer N. No wait, N is too big; take a positive integer k."

Here is a non-exhaustive classification of math jokes:

Puns on mathematical terminology

Mathematical reasoning in non-mathematical setting

Twists on expectations

Meta-jokes approached in a mathematical mode of enquiry

A joke can belong to more than one classification. For example, the "Dog and cow knot theorists" has both puns and a twist on expectations.

By the way, I would exclude jokes which are purely made on stereotypes, like the above joke on extrovert mathematician, because I don't find it funny.

I leave with one of my favorite meta-jokes:

"How many members of a certain demographic group does it take to perform a specified task? A finite number: one to perform the task and the remainder to act in a manner stereotypical of the group in question."

(25)
The epsilon joke isn't funny. It would be funny if it read "epsilon <= 0". - Loop Space

(7)
Still don't get the epsilon joke, with or without =. - mathreader

(8)
The joke is that epsilon almost always stands for a small positive real constant, e.g. in the epsilon-delta definition of continuity. - Qiaochu Yuan

(8)
The classification provided by the meta-joke is quite precise :) - Pandora

(2)
⁺¹ for jokes classification. - Hi-Angel

22

[+65]
[2009-10-19 00:30:44]
David Zureick-Brown

I received today this comment about a paper:

3 lines before section 2.1:
A few typos: corresponds, 5-isogeny
(I guess a 5-isogenie grants you five wishes?)

(177)
a 5-isogenie grants you 5 identical wishes. - Michael Lugo

(4)
When the comments get more upvotes than the answer. - Simply Beautiful Art

23

[+63]
[2009-11-04 04:45:07]
Andy Mikula

Q: What is non-orientable and lives in the ocean?
A: Möbius Dick...

A mathematician organizes a raffle in which the prize is an infinite amount of money paid over an infinite amount of time. Of course, with the promise of such a prize, his tickets sell like hot cake.

When the winning ticket is drawn, and the jubilant winner comes to claim his prize, the mathematician explains the mode of payment: "1 dollar now, 1/2 dollar next week, 1/3 dollar the week after that..."

"The number you have dialed is imaginary. Please, rotate your phone by 90 degrees and try again..."

A famous mathematician gave a talk (maybe about mathematical physics), after which an as famous physicist sitting in the first row got up, and loudly declared: "That's all nice, but without mathematics, research in physics would be maybe a week behind the state it is now!"

The famous mathematician responded: "Yes, the week god needed to create the world."

(34)
<< The great probabilist Mark Kac (1914-1984) once gave a lecture at Caltech, with Feynman in the audience. When Kac finished, Feynman stood up and loudly proclaimed, "If all mathematics disappeared, it would set physics back precisely one week." To that outrageous comment, Kac shot back with that yes, he knew of that week; it was "Precisely the week in which God created the world." >> - Cristi Stoica

25

[+60]
[2009-10-19 01:26:40]
Michael Kleber

Q: How many mathematicians does it take to change a light bulb?

A: One: she gives it to three physicists, thus reducing it to a problem that has already been solved.

26

[+59]
[2009-10-21 01:06:26]
Scott Morrison

An engineer, a physicist and a mathematician are driving through the high country in Scotland. Atop a hill, they see a black sheep.

The engineer says: "All sheep are black!"
The physicist says: "No, no, some sheep are black."
The mathematician: "At least one sheep is black on at least one side."

Here is a joke I invented (based on a famous one) and had mixed reaction.

A young mathematician comes to present to a famous mathematician his conjecture and ideas. "You are absolutely wrong," the famous mathematician dismissed the young one. Next enters another young mathematician and presents precisely the opposite conjecture. "You are absolutely wrong" replies the famous mathematician. The famous mathematician's wife interferes. "How could you tell both of them that they are wrong," she sais. "They have made completely opposite claims, one of them must be right!" "You are also wrong," replied the famous mathematician.

(8)
LOL ... I upvoted it! Upon the same theme, the (Hungarian) physicist Val Telegdi was fond of the following (Hungarian) maxim: "It is not enough to be rude; one must also be wrong!" :) - John Sidles

Q: What do you call it when you're trying to prove that a map is injective, but you just can't do it?

A: Monic fail.

(36)
I couldn't, for the life of me, figure out how automorphisms were supposed to be useful on car trips. After all, it doesn't really help to show that the landscape outside your window is non-trivially equivalent to itself; what you're really interested in is showing that it's equivalent to some smaller object you have within your vehicle. Then I realized it's a pun. - Tanner Swett

30

[+46]
[2009-10-22 19:55:00]
George Lowther

Do good math jokes exist? Under the axiom of choice, sure. But it's not possible to find an explicit example.

31

[+42]
[2009-10-19 15:51:47]
Greg Muller

An engineer hears that a famous mathematician will be giving a public lecture, and always having a soft spot for math, he attends. The mathematician then talks at length about all sorts of amazing phenomena that happen in 17 dimensional space. The engineer, amazed at this mathematician's intuition for 17 dimensional space, goes up to him afterwards and asks 'How do you picture 17 dimensions?", to which the mathematician answers 'Oh, its easy. Just imagine n-dimensional space, and set n equal to 17.'

My dad (an engineer) loves that joke.

32

[+41]
[2009-11-23 05:30:45]
AndrewLMarshall

What did the forgetful functor do for his stoner friend?

He left adjoint as a free object.

33

[+36]
[2009-12-13 07:32:18]
evan

After introducing general topological spaces, the professor began to introduce the notion of convergence without a metric. He turned around and said,

"I have no balls."

A hit for months.

Hmm, P.M.´s lecture on Functional Analysis? - M.G.

It's classical. Like the professor saying that "$\mathbb{R}^n$ has got balls" - Qfwfq

34

[+33]
[2009-10-21 22:34:04]
Gabe Cunningham

There are 10 types of people in the world: those who understand binary, and 9 others.

(19)
From a lecture in grad school years ago: There are three kinds of people in the world: those who can count and those who cannot. - José Figueroa-O'Farrill

35

[+33]
[2009-11-04 04:26:18]
Ross Churchley

Less of a joke than an observation, but...

I've always found it appropriate that online identity thieves are in the business of stealing ones and zeroes.

Ha! I only got this on my third readthrough of this list. - Cam McLeman

I still don't get this... - Qiaochu Yuan

(20)
@Qiaochu Yuan: One and zero are identities. :-) - shreevatsa

(1)
Bwahaha! I like this one... :) - rschwieb

36

[+32]
[2009-11-04 00:11:47]
Eric Wofsey

Q: What's purple and commutes?
A: A dead baby in a suitcase.

Q: What's purple and commutes and has a certain number of followers?
A: A dead baby Jesus in a suitcase.

(5)
Excellent! Only a mathematician would get this! - Steven Gubkin

(24)
a mix of math jokes with dead babies, and they said it could'nt be done... - Sean Tilson

The water receded and the Ark came to rest upon the land. Noah opened the doors and commanded the animals, “Go forth and multiply.” The animals slowly departed the Ark except for two snakes that remained in the back. Again Noah proclaimed ,“Go forth and multiply” yet the two snakes did not move. Noah walked to the back of the Arc and asked, “Why have you not followed my command”.? The snakes answered, “Noah, we can’t because we are Adders.”

Noah then went out upon the land and felled several large trees; from these trees he made a four legged platform. He then went inside the Arc and carried the snakes outside and upon placing them on the platform, his words became true.

As everyone knows … Adders can multiply using log tables.

A beautiful cringe - galois

38

[+29]
[2009-10-19 06:25:23]
Alison Miller

Perhaps the question should be, not "Do good math jokes exist", but "are they unique"?

(10)
I think there's only one isomorphism class of math joke. - userN

(51)
But sadly, it has non-trivial automorphisms. - Andrew Critch

(2)
Let's classify the category of math jokes. Is it additive? abelian? triangulated? tannakian? a topos? - David Corwin

39

[+25]
[2009-10-21 22:17:38]
gowers

My favourite is supposedly a joke made by a mathematician who was interviewing a not very good graduate student who was taking generals. The interview was going badly, so to make the student feel better the mathematician asked him for an example of a compact topological space. "The reals?" suggested the student, to which the mathematician replied, "Which topology were you taking?"

(45)
I heard this one, and with the names of those involved, but slightly differently: there were two examiners and, in desperation, one asked for an example of a compact space to which the answer "the reals" was offered. The second examiner, in a vain attempt to help, then asked "In what topology?". - Loop Space

(64)
This might be apocryphal, but someone I know claims to have seen the paper. In a Topology exam, a question asked whether two spaces X and Y (defined in the question) were homeomorphic. One student answered: "X is, but Y isn't." - José Figueroa-O'Farrill

(4)
Some years ago, David Letterman had a series of segments called "Over Our Heads" where he invited experts in various technical disciplines to come on and tell specialized jokes. Mike Roth (now a professor at Queens) knew one of the writers and was invited to tell a math joke. Andrew's version of the oral exam/topology of the reals joke is the one he told. Andrew's version of the - D. Savitt

(8)
Approximately two and a half years later I see that I didn't write what I intended to write. I did of course intend to write "compact" -- or else the joke makes no sense. In other words, Andrew Stacey's version is what I intended (except that in my version there was just one examiner). - gowers

(4)
Few years ago I failed a linear algebra student which replied to my question: "What is the dimension of the plane?" with "Infinity?". Only after she had left I realized I should had asked her: "Over which field?" - Vít Tuček

(1)
@JoséFigueroa-O'Farrill I have seen the phenomenon firsthand. On a first-year algebra exam, Prof. Artin wrote down three matrices and asked the students to prove that they were conjugate. A handful of students did the following: they proved first that the first matrix was conjugate; then that the second was conjugate; and finally that the third was also conjugate... - Lily Chung

40

[+25]
[2009-10-23 22:40:17]
Manny Reyes

One of my favorites. It's about a statistician - close enough for me. (I found this version of the joke
here
[1])

A physicist, an engineer, and a statistician were out game hunting. The engineer spied a bear in the distance, so they got a little closer. "Let me take the first shot!" said the engineer, who missed the bear by three metres to the left. "You're incompetent! Let me try" insisted the physicist, who then proceeded to miss by three metres to the right. "Ooh, we got him!!" said the statistician.

[1] http://www.phy.ilstu.edu/~rfm/107F07/EPMjokes.html

41

[+23]
[2009-10-19 06:34:24]
Mikael Vejdemo-Johansson

I find the observation that the grade school carry operation from addition-with-carry forms a non-trivial degree 1 cocycle in the group cohomology of Z/10 a pretty good joke embedded in mathematics.

I really don't get the non-mathematical part of this joke. What is "the grade school carry operation from addition-with-carry"? - jmc

The Hilbert, or axiomatic, method. We place a locked cage at a given
point of the desert. We then
introduce the following logical
system.

Axiom I. The class of lions in the Sahara Desert is non-void.

Axiom II. If there is a lion in the Sahara Desert, there is a lion in the
cage.

Rule of Procedure. If p is a theorem, and "p implies q" is a
theorem, then q is a theorem.

Theorem I. There is a lion in the cage.

The method of inversive geometry. We place a spherical cage in the desert, enter it, and lock it. We perform an inversion with respect to the cage. The lion is then in the interior of the cage, and we are outside.

The method of projective geometry. Without loss of generality, we may
regard the Sahara Desert as a plane.
Project the plane into a line, and
then project the line into an interior
point of the cage. The lion is
projected into the same point.

The Bolzano-Weierstrass method. Bisect the desert by a line running N-S. The lion is either in the E portion or in the W portion; let us suppose him to be in the W portion. Bisect this portion by a line running E-W. The lion is either in the N portion or in the S portion; let us suppose him to be in the N portion. We continue this process indefinitely, constructing a sufficiently strong fence about the chosen portion at each step. The diameter of the chosen portions approaches zero, so that the lion is ultimately surrounded by a fence of arbitrarily small perimeter.

(5)
It's hard to beat the following for simplicity (or agreement with mathematical practice): go into the cage, lock it, and declare yourself to be on the outside. - Hugh Thomas

Yeah, the method of inversive geometry is one of my favorites. - las3rjock

47

[+17]
[2009-10-30 13:25:53]
Humberto Rafeiro

The continuous functions are having a
ball. At the dance floor, cosine and
sine are jumping up and down, and the
polynomials are forming a ring. But
the exponential function is standing
separately the whole evening. Due to
sympathy for it, the identity joins it
and suggest: "Come one, just integrate
yourself!" – "I've tried that
already", answers the exponential
function, "but it didn't change a
bit!"

another one

Why the mathematician named his dog
"Cauchy"? Because he leaves a residue
at every pole

(2)
Tom Lehrer was a genious. His song "Werner von Braun" is absolutely brilliant. - GMRA

(1)
I hope Tom Lehrer still is a genius - I believe he's still alive :-) and yes, that's absolutely true. His wordplay and clever humor are really masterful. - Alon Amit

I didn't know he was a mathematician! :) - Vectornaut

(8)
He was my calculus section man in 1960 and apparently a democrat, since he proposed as an example of proof by vacuous hypothesis the statement: "all progressive republicans wear green eyeshades". - roy smith

49

[+14]
[2009-11-07 01:44:27]
Amy Pang

A friend made this up recently (I prefer the first half on its own):

"No meal is complete without soup. But you have to order it first."

Also I like this meta-joke, also by a friend (who didn't understand the original):

"What's purple and commutes? An abelian eggplant."

EDIT: one more, by Elizabeth: "Does this Hausdorff measure make me look fat?"

I like the soup one. - Steven Gubkin

50

[+12]
[2009-11-06 13:33:15]
Gil Kalai

A millionaire is trying to scientifically develop the best racing horse. He asked a biologist, veterinary, trainer, and a mathematician. The biologist gives him an advice about which type of horse to cross with which other type, the veterinary advices on how to feed the horse, and how to keep him healthy, the trainer explains how to physically train the horse. The mathematician does not reply. After a few weeks the millionaire meets the mathematician and it looks that the mathematician did not sleep much in recent days. Do you have a solution for me, ask the millionaire? It is a difficult problem, answers the mathematician, but I think I have a satisfactory solution to the case of spherical horses.

(8)
The version I know of this joke has a physicist proposing a solution for spherical horses. The mathematician thinks long and hard, and announces that she has solved the problem: she can prove that, for every horse race, there exists a unique winner. - Nate Eldredge

I excuse my english if you spot some flaws...., since this is my first post here I thought it would be nice to share some neat jokes.

1) A mathematician, a physicist and an engineer were out in the countryside when they met a farmer trying to build a fence. They introduced themselves and the farmer asked them if they could help him shape the fence so he would get as much space as possible within it. The engineer stepped forward and said, that it would be best for the farmer to make the fence square, that would be easiest. The physicist then said that it would be better to make it as a circle, because then he would get as much space as possible. The mathematician laughed and said that you can get a lot more space then that! He took some pieces of fence and rolled it around himself, then he defined himself outside the fence!

2) Infinitely many mathematicians walked into a bar, the first one asked for one beer, the next one asked for half a beer, the third one asked for a quarter of a beer and the fourth one asked for one eight of a beer, then the bartender said :"screw this" and filled two glasses of beer!

3) An engineer was working on a problem when suddenly his trash bin caught fire. He immediately grabbed the fire extinguisher and put out the fire. In the next room a physicist was also working on a problem when his trash caught fire, he thought, fire extinguisher block oxygen from the fire, ergo fire is put out. So he grabs the fire extinguisher and puts out the fire. In the third room there was a mathematician working on a problem, his trash bin also caught fire so he looked at and thought, problem has a solution, and continued working!

(6)
For the second joke, it's even better if the bartender says "you need to learn your limits!" - ಠ_ಠ

Haskell is a programming language (named after the logician Haskell B. Curry). It has been developed by academia (not by industry or market), and most motivations behind its creation was cleanness and purity. And it is based directly on lambda calculus, type theory, combinatory logic. Many of the programmer practice in it is based on category theory and algebra.

[1] http://www.willamette.edu/~fruehr/haskell/evolution.html

56

[+9]
[2009-11-13 07:49:53]
Greg Kuperberg

I once ad-libbed this one. (Alas, it is a late entrant.)

Q: Why is it important to study Verma modules of Lie algebras?

A: The most widely used modules of Lie algebras and Lie groups are finite-dimensional irreducible representations, the Weyl modules. Of course, you should learn them first when you study representation theory. But they are only the tip of the iceberg.

(2)
Care to explain the joke to non-specialists? - Boris Bukh

(12)
If you draw a highest-weight Verma module containing a finite-dimensional representation, e.g. for su(3), it is an infinite iceberg with a finite tip. I suppose that the joke is obscure, even for more most mathematicians. - Greg Kuperberg

I first heard this on an episode of the Big Bang Theory, I don't know the origin.

The physicist asks the mathematician: "Why did the chicken cross the road?"

The mathematician ponders a while and then replies: "I have a solution, but it only works for a spherical chicken in a vacuum."

59

[+4]
[2009-10-21 06:54:34]
diab

An infinite number of mathematicians walk into a bar. The first one orders a beer, the second one orders half a beer, the third one a quarter of beer and so on. After a while of this happening, the bartender says "Come on guys! So many people and not even a couple of beers??".

60

[+4]
[2009-11-26 22:21:56]
Colin Diemer

Q: What did the threefold blown up at two points say while waiting in a long line for a restroom?

(8)
What's purple, commutes, and is worshipped twice a night? A bi-nightly venerated Abelian grape. The other answer to "what's purple and commutes?", for the Chicagoans and ex-Chicagoans out there, is "the Evanston Express". - Hugh Thomas

(33)
They are not posted because they are not good, maybe? :P - Mariano Suárez-Álvarez

(16)
Seen on a restroom wall in the Berkeley math dept.: What's brown and commutes? An abelian poop. - S. Carnahan

Consider the following scenario: A room with a sink at the far end with a working cold water faucet plus a table with the following items on top – small bucket, ring stand, Bunsen burner, and a pack of matches. The problem is to boil water.

If the individual picks up the bucket from the table, walks to the sink and fills the bucket from the faucet, brings it back to the table, sets it on the ring stand, puts the Bunsen burner under the stand, and then lights the burner and waits for the water to boil … this establishes the base line but does not separate which it the Physicist and which is the Mathematician.

Test scenario 2: The bucket is now sitting on the floor under the table and the problem is again to boil water.

If the individual picks up the bucket from under the table, walks directly to the sink and fills the bucket from the faucet, brings it back to the table, sets it on the ring stand, puts the Bunsen burner under the stand, and then lights the burner and waits for the water to boil … this proves that this individual is the Physicist.

However, if the individual picks up the bucket from under the table and places it back on top of the table thus reducing the current problem to a form that they have previously solved … this proves that this individual is the Mathematician.

(1)
There's a sequel to this when the first scenario is putting out fire when the house is burning and the second is when the house is not burning. - Zsbán Ambrus

There was a simple version: Scenario2: the bucket was filled with water at the beginning. The one who boils it directly was physicist, the one who pours the water out to reduce it to a solved problem was mathematician. - Wilson of Gordon

64

[+3]
[2009-10-26 00:48:57]
John Goodrick

Q: Why was 3 afraid of 5?

A: Because "5 8 13."

(Works better when you actually say it out loud...)

(6)
I prefer the reductive version "Why was 8 afraid of 8?" - Richard Dore

(11)
Hey, if you do that and allow plurals, then you can make an alternative to the "buffalo buffalo buffalo..." sentences using all 8s. e.g. 8s8s888s (the eights that eights ate, ate eights...) - Elizabeth S. Q. Goodman

For actual humour, rather than simply bad puns, I recommend the books:

A Random Walk in Science

More Random Walks in Science

As well as the odd bad pun, they also contain many anecdotes demonstrating that scientists (and mathematicians) are also human. A few that have stuck in my memory: just about every "mathematics of big game hunting" method, the various "proof by ...", a (genuine!) article co-authored by a cat, and a disturbing article on refereemanship.

In a math party, all were having a good time. y was the dj, everybody was Riemmanly drunk. Then, when the x saw e^x on a corner crying, he asked:
- Hey e^x, why don't you integrate ?
- Because I keep always the same!!!

Check out the book
777 Mathematical Conversation Starters
[1] by John de Pillis. The subject of the book is mathematics topics to talk about, but it is also full of interesting quotes, jokes, and cartoons.

[1] http://rads.stackoverflow.com/amzn/click/0883855402

70

[-1]
[2009-10-26 00:10:53]
Diego de Estrada

If we can formalize the property of "being a good math joke" good enough to construct a Turing Machine that checks it, then I think we can conclude they don't exist.

The reason is that in that case we can construct a Turing Machine (say of length N) that checks each possible string, and stops only if a good math joke was found.
The
busy beaver function
[1] on N establishes an upper bound for the number of strings the machine needs to check until we can conclude that it wouldn't halt (and therefore no good math jokes exist).

Based on empirical evidence, it may be possible that all those cases have already been checked (with negative answer), which implies my thesis.

(I'm being ironical, I like much of the jokes posted in here :P)

[1] http://en.wikipedia.org/wiki/Busy_beaver

71

[-3]
[2009-10-19 00:16:11]
William Mauritzen

A mathematician in a job interview was asked, "We need to see what kind of attitude you have toward problem solving. So tell us, is the glass half empty or half full."

His reply, "It's 1-x."

-William Mauritzen

72

[-6]
[2009-11-03 22:17:20]
joe s

Q: What's purple and commutes?
A: An abelian grape!

73

[-9]
[2009-10-19 12:24:00]
Martin Peck

As it would be impossible to prove that good math jokes don't exist I would have to say that the probability is better than zero.

74

[-17]
[2009-10-22 13:10:58]
foobar

12 ? The least integer that symbolizes all integers just by itself. Successors: 123, 1234...